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I have an arduino with a simple 3-pin IR receiver like you would find at radio shack. The receiver works fine when the power supply to the arduino is 6 AA batteries, but not when the power supply is a wall plug with 7.5V DC. It seems to work for a few seconds, then not at all. I'm using the IRRemote library here: http://www.arcfn.com/2009/08/multi-protocol-infrared-remote-library.html

To further help describe the problem, the Arduino is controlling a bunch of LEDs, and when I use PWM to turn down the brightness of these LEDs, the IR receiver ceases to work as well, either when battery powered or wall powered. When the PWM is not being used and the LEDs are full on, it's not a problem.

I'm not sure how to debug or fix this. I'm sure that the IRRemote is using a different timer than the PWM, and the power source exhibiting the problem when the PWM is off confirms that that's not the root cause. I suspect that there may be some kind of noise introduced by the wall power supply or the rapid switching of the LEDs. Both the receiver and all of the LEDs are tied to the same ground pin of the Arduino. What can I do to separate or filter the receiver so that it is not affected by the power supply or PWM?

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The datasheets of most IR receivers recommend some minimal filtering of the power supply, check for instance http://www.sharpsma.com/webfm_send/1351 p 4 : 47 Ohm / 47uF.

Even with such power filtering I have experienced that an IR receiver on one of my boards worked much better when powered from a wall-wart+7805 compared to being powered (directly) from USB.

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    \$\begingroup\$ If the receiver is so sensitive to power supply noise it may be a good idea to power it from an LDO which reduces the +5V to a value like, say, +4V. Most Vishay IR receivers, and also the Sharp type Wouter mentions, operate from 2.7V. The LDO may also require an input capacitor smaller than 47μF (which is huge!). LDO-wise I'm a fan of the Seiko S-812C, which has excellent specs and doesn't even need an output cap. \$\endgroup\$ – stevenvh Jul 4 '11 at 17:13
  • \$\begingroup\$ I think you're right. Thanks for the tips @stevenvh; trying to get the filter/regulator working now. \$\endgroup\$ – Bob Baddeley Jul 18 '11 at 22:06
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Which Arduino do you have?

I took a look at the Uno schematic and it uses MC33269 series regulators. They'd need voltage of at least 6.35 V to guarantee reliable operation. The rectifier needs additional 1.1 V, so minimal input voltage should be 7.45 V, which is pretty close to your input voltage. Make sure to make input voltage measurements when the problems appear.

Be sure to check what the supply actually gives with a multimeter, because a small voltage drop may be enough to bring the system out of regulation.

Next, check the current consumption and make sure that it is within limits of the on-board regulators. It should be well below 1.6 A.

At this point, if you still have a problem, it probably isn't related to the external power supply.

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  • \$\begingroup\$ Interesting thoughts. It's an Uno. I switched to a different power supply and it reads 11.5V on the multimeter. The Kill-a-watt says it's consuming ~200mA and ~11Watts. \$\endgroup\$ – Bob Baddeley Jun 23 '11 at 22:35
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It sounds like your wall adapter might be unregulated, or overloaded. Drawing largish pulses of current such as blinking a string of LEDs may cause its output voltage to fluctuate significantly - enough to annoy a sensitive part like an IR receiver anyway. You could have the same problem when running from battery if its internal resistance is high enough. You might even see it if the power wiring is too high resistance, like your battery holder has cheap metal in the spring, wires are too narrow or too long, your board traces for power are too narrow, or some other component in the power path adds too much resistance.

As @stevenvh points out, you probably need a voltage regulator on the IR receiver to give it cleaner power. An IR part that operates from 2.7V was likely designed to run from an LDO that has the 3.3V rail as its input (the output being something like 2.7-3.0V depending on the LDO), although the LDO might be powered from the battery if there's no other regulator in the design.

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